code: def __getitem__(self, idx):
      dataset_idx = self.dataset_index[idx]
      sample_idx = self.dataset_sample_index[idx]
      return self.datasets[dataset_idx][sample_idx]
  
file_path: NeMo/nemo/collections/nlp/data/language_modeling/megatron/blendable_dataset.py
imports: import time
  import numpy
  import torch
  from nemo.utils import logging
  from nemo.utils.app_state import AppState
label_desc: Use image node_id 3 for calling the BlendableDataset obj's underlying member method code with example usage: obj.__getitem__(idx) and returns: self